One reason for the ever increasing popularity of computers has been the advances in the quality of the images that may be displayed thereon. The ability to display high quality images has resulted from many different developments in the field of computer science and electronics. More specifically, the availability of low-cost computers having large amounts of dynamic memory, large mass storage devices, high quality/resolution display monitors, and fast central processing units (CPUs) has allowed for the widespread use of computer images having sufficient resolution to be clear and enjoyable to view without requiring an undue amount of computer processing to effect the display thereof. Furthermore, the increased clarity of computer images has allowed doctors, dentists, architects, engineers, and others to utilize computer images in the performance of their respective duties. For example, x-ray data may now be displayed on a computer monitor with sufficient resolution and with all the required colors or shades of grey to allow a doctor or dentist to safely and effectively evaluate medical/dental conditions.
Unfortunately, with the above-noted increased quality of computer images comes a corresponding increase in file size. In most instances, the image data is compressed so that it does not occupy an excessive amount of storage space. However, the more compressed an image file is, the more time and processing power it takes to decompress the file for viewing the image. Also, while "lossy" compression techniques (compression techniques wherein some aspect of the original image data is discarded) allow for faster and increased compression of the data, in certain applications, such as when x-ray images are being used for medical diagnosis, lossy compression techniques and the computer images resulting therefrom, are generally unacceptable. Therefore, an x-ray image, for example, when of a certain high resolution and when represented with a sufficiently "deep" greyscale, may occupy more space than is available on a single piece of storage media such as a single computer diskette.
The increasing size of computer image data files has created a need to provide a method for storing and retrieving image data from a single image to and from multiple storage locations in a simple and effective manner. For example, a first storage medium (diskette, magnetic tape, fixed disk drive) may contain a limited amount of available space which is less than the space needed to store an image. There has been found a need to provide a method for storing a portion of the computer image to the available space on the first storage medium, and to thereafter store the remaining image data to additional storage media (which may be several, and may be the same type or different from the first storage medium). There has likewise been found a need to provide a method for later retrieving data that has been stored "across" multiple storage media in this manner. Furthermore, it would be most desirable to allow the computer image data to be retrieved from the various storage locations without regard to the order in which the retrieval occurs.
Known methods and image file formats do not allow the image data of a single image to be stored on separate pieces of storage media, whether diskettes, floppy diskettes, magnetic tapes, fixed disk drives, or any combination thereof. This results from the fact that the image data is preceded by image "header" information relating to the characteristics of the image that is necessary to properly retrieve the image from its storage location. It can be seen, for example, simply continuing image data from a first diskette to a second diskette causes the image data on the second diskette to become disassociated from necessary header information located on the first diskette, thereby rendering the information on the second diskette irretrievable using conventional techniques.
As is noted above, available fixed disk drives (also referred to as hard disk drives) are capable of storing massive amounts of data, often one to two gigabytes (GB), or more. Therefore, it is a less common occurrence that an image data file will not fit onto the available space of a fixed disk drive. However, when an image data file must be stored to another medium (the previously mentioned diskettes for example) for archival and/or transport of the image data, difficulty arises when the size of the image file exceeds the available amount of space on the medium. For example, it is currently impracticable to transfer large image data files across telephone lines using modem technology due to the relatively low data transfer rates currently available. Therefore, when the transportation of image data is required, the image data is commonly stored on a diskette and the entire diskette is delivered to the image recipient. The recipient may then load the diskette into his or her computer for viewing. Most 3.5 " computer diskettes are currently capable of storing in the range of 1.4 megabytes (MB) of data. Therefore, it can be seen that as the image file size (whether compressed or not) is greater than 1.4 MB, more than one diskette must be utilized to store the image data. For example, a 4 MB image file will require the use of three 1.4 MB diskettes. As noted, known image file formats are incapable of allowing an image file to be stored to or "across" multiple pieces of storage media.